The Sura's name is in reference to an argument between the Prophet Moses and the Israelites over a cow they should sacrifice in order to know the murderer of a slain man (see 2:67-74). (Not to be confused with the popular biblical incident where Moses clamped down on the Israelites' worshipping a cow idol - which is also pointed out in this sura.)
It is a Madinan sura; most of it was revealed during the first two years after the Hijra, but some sections (for instance, the verses prohibiting interest on loans) were revealed later, and the last three verses had been revealed in Mecca. It addresses a wide variety of topics, including substantial amounts of law, and retells stories of Adam and Moses and Abraham. A major theme is guidance: urging the pagans and Jews of Madina to become Muslim, and warning them and the hypocrites of the fate God had visited in the past on those who failed to heed his call.
It appears to be one of the earliest suras (with an-Nisa and some others) to be mentioned by name in a non-Muslim written source. John of Damascus (~730s) speaks of "the text of the Cow", and the Syriac Disputations of a Monk of Beth Hale and an Arab Notable (date hard to determine, but apparently post-710) has the monk saying "I think that for you, too, not all your laws and commandments are in the Qur'an which Muhammad taught you; rather there are some which he taught you from the Qur'an, and some are in surat albaqrah and in gygy (Injil?) and in twrh (Torah.)"
